222 ANNUAL OF SCIENTIFIC DISCOVERY. 



ists well know that heating and cooling repeatedly a solution of glue, 

 (gelatine,) in contact with the air, it looses its property of becoming a 

 jelly. M. Gmelin has shown, that a solution of fish glue in a sealed 

 tube, placed in a water bath heated to the boiling point for several 

 days, exhibits the same phenomena, L e. the glue remains liquid, does 

 not gelatinize upon cooling. 



The change effected, is one of the most difficult problems to resolve, 

 of organic chemistry. It appears to be a product of the action of the 

 oxygen of the air and the water upon the glue, as demonstrated from 

 the action of a small quantity of nitric acid, on a solution of strong 

 glue. We know that on treating gelatine with an excess of this acid 

 in the presence of heat, it is converted into malic and oxalic acids, fat, 

 tannin, &c. This does not occur when we treat the glue dissolved in 

 its weight of water, with a very small quantity of nitric acid ; we 

 obtain only a strong glue which preserves a long time its primitive 

 qualities, and which no longer has the property of gelatinizing. In this 

 manner the glue sold in France under the name of liquid and 

 unchangeable glue, is fabricated. This glue is exceedingly conven- 

 ient for cabinet makers, joiners, pasteboard manufacturers, toy makers, 

 &c., since it can be used cold. It is prepared as follows : 



Dissolve two pounds of strong glue in one quart of water in a glue 

 kettle, or in a water bath, when the glue is entirely melted, add 

 little by little, to the amount often ounces of strong nitric acid. This 

 addition produces an effervescence due to the disengagement of hypo- 

 nitric acid, when the whole of the acid is added, remove the vessel 

 from the fire, and leave it to cool. I have preserved glue thus pre- 

 pared, more than two years in a stoppered flask, without its under- 

 going any alteration. This liquid glue is very convenient in chemical 

 operations. I have employed it with advantage in my laboratory, for 

 the preservation of different gases, the same as lute, covering the little 

 bands of linen with the glue." 



PERFUMERY AND THE ARTIFICIAL EXTRACTS OF FRUIT. 



DR. PL A YF AIR, in his lecture on the Results of the Great Exhi- 

 bition, thus briefly notices a new class of perfumes and essences, 

 which of late have attracted no little attention. 



Much aid has been given by chemistry to the art of perfumery. It 

 is true that soap and perfumery are rather rivals, the increase' of the 

 former diminishing the use of the latter. Costly perfumes, formerly 

 employed as a mask to want of cleanliness, are less required now that 

 soap has become a type of civilization. Perfumers, if they do not 

 occupy whole streets with their shops, as they did in ancient Capua, 

 show more science in attaining their perfumes than those of former 

 times. The jury in the exhibition, or rather two distinguished chem- 

 ists of thaf jury, Dr. Hoffman and M. De la Rue, ascertained that 

 some of the most delicate perfumes were made by chemical artifice, 

 and not, as of old, by distilling them from flowers. The perfume of 

 flowers often consists of oils and ethers, which the chemist can com- 



